Entwurf von Flüssigkeitsbehältern

Design of Liquid Retaining Structures – Remarks on the Rules of the Guideline “Watertight Concrete” The use of watertight concrete structures is regulated by the guideline “Watertight Concrete” of the German Committee of Reinforced Concrete, especially requirements on the serviceability limit states. The scope of the guideline is valid for liquid retaining structures too. The essential characteristic of those structures is their defined tightness. Design concepts in order to fullfill requirements on durability of concrete tanks are discussed. Moreover, recommendations due to the design of moderate prestressed reinforced concrete tanks are given, containing the durable filling of planned cracks. Design aspects of the European Standard EC 2 Part 3 are discussed too.     

Bauteile aus Stahlfaserbeton und stahlfaserverstärktem Stahlbeton

Mit der zu erwartenden Einführung der Richtlinie “Stahlfaserbeton” des Deutschen Ausschuss für Stahlbeton (DAfStb) entsteht für den Verbundwerkstoff Stahlfaserbeton ein neues, breites Spektrum an zusätzlichen Anwendungsmöglichkeiten. Durch die Wirkung der Fasern im Beton können nach Überschreitung der Betonzugfestigkeit nennenswerte Kräfte zwischen den Rissufern übertragen und bei der rechnerischen Erfassung des Tragverhaltens berücksichtigt werden. Im Aufsatz werden Vorgehensweisen, Hilfsmittel und ein auf Tabellenkalkulationen und Optimierungsmethoden basierendes Programm zur Biegebemessung und Verformungsabschätzung von Querschnitten und Systemen aus Stahlfaserbeton und stahlfaserverstärktem Stahlbeton entwickelt. Grundlage sind die bekannten Bemessungsansätze und ‐hilfsmittel für Stahlbetonquerschnitte. Die Anwendung der Hilfsmittel – auch für Verformungsabschätzungen auf Basis nichtlinearer Verfahren – zeigen zwei Beispiele. Structural Elements of Steel Fibre Reinforced Concrete with or without Bar Reinforcement Tools for Design and Deflection Estimations according to the Guideline “Stahlfaserbeton” by DAfStb The expected release of the guideline “Stahlfaserbeton” by ‘German Committee for Reinforced Concrete’ (DAfStb) offers a wide application range for the composite material steel fibre reinforced concrete (SFRC). Due to additional steel fibres in concrete considerable tension forces can be transferred between crack edges after reaching plain concrete's tensile strength. These forces can be accounted for in calculation of load bearing capacity. Adapted from common design methods and tools for plain reinforced concrete new procedures, tools and a computer application – based on spreadsheet analysis and optimisation methods – for SFRC are presented in this article. These allow for both bending design as well as deflection estimation of crosssections and structural systems made of SFRC with and without additional rebars. Their application – also in case of deflection estimation using non‐linear methods – is demonstrated in two elaborated examples.     

Philosophie des neuen DBV/BDZ‐Merkblattes “Sichtbeton”

Philosophy of the new DBV/BDZ‐Code of Practice “Architectural Concrete” In August 2004 the Deutsche Beton‐ und Bautechnik‐Verein E.V. (DBV) and the Bundesverband der Deutschen Zementindustrie e.V. (BDZ) published after 1977 and 1997 the third edition of the Code of Practice "Architectural Concrete". For the first time four classes SB 1 to SB 4 are defined which differ in demands on texture, porosity, steadiness of shade, evenness and quality of construction joints and formwork joints. Further demands concern test surfaces. In the main part comments on design and bidding procedure of architectural concrete and on their implementation are given. They are based on experiences which were made on prominent buildings on architectural concrete during the last years. The last part deals with the assessment of the architectural concrete surface. Principle is that the first and decisive criteria is the overall impression.     

Instandsetzung von Rissen in Stahlbetonbauteilen nach einer außergewöhnlichen Einwirkung

Repair of Cracks in Reinforced Concrete Structures after Accidental Action Accidental loads – for example an earthquake, a vehicle impact or blast and shock waves due to detonations – lead to local damages in RC‐structures. Both the damage assessment as well as the repair of damaged reinforced concrete are important topics with respect to a durable use of infrastructure. After damage assessment a further step focuses on the repair of damaged structural concrete. Therefore fundamental investigations concerning the use of different repair methodologies have been carried out with respect to damage after accidental action. The grouting techniques used focus on the repair of cracks, the concretes microstructure and the weakened bond between reinforcement bars and concrete in the surrounding damage zone. Furthermore this contribution includes applicationoriented experimental investigations concerning the repair of reinforced concrete components by grouting and a discussion of the appropriateness for repairing RC‐structures damaged by accidental action.     

Alpenquerende Tunnel: Prüfsystem für Betonmischungen beim Gotthard‐Basistunnel

Gotthard Base Tunnel: Testing System for Concrete Mixtures AlpTransit Gotthard is a future‐orientated project for a high speed railway through the Swiss Alps. The base tunnel under the St. Gotthard massif – with 57 kilometre the world's longest tunnel – is the core structure of the new transalpine Gotthard railwayline. This 21st century project will significantly improve passenger travel and freight transport in the heart of Europe. The main features of the project and the processing of the excavated material will be presented. The applied testing system for concrete mixtures, the contractual conditions and the implementation on site will be explained. The construction of the Gotthard Base Tunnel will produce approx. 24 million tonnes of excavated rock. This huge amount of material has a large potential to be converted into concrete aggregates. Already in 1993 an innovative testing programme for concrete mixtures was launched in order to prove that high‐quality concrete can be produced using TBM‐excavated material. The permanent testing on site ensures, that the produced concrete will meet the high requirements in tunnel construction.     

Beschichtungen auf direkt befahrenen Tiefgaragenbodenflächen von Weißen Wannen. Physikalische Beanspruchungen – Planungsgrundlagen – alternative Beschichtungsvarianten

Coatings on directly vehicle‐carrying floor slabs of watertight concrete constructions in underground carparks physical stresses – design codes – alternative coating systems According to DIN 1045‐1 directly vehicle‐carrying park decks have to be realized with additional measures (crack‐bridging coating systems). At least surface protection system 11 (SPS 11) according to the Guidelines for the Protection and Repair of Concrete Components of the German Committee on Reinforced Concrete (DAfStb) are among others a possibility to meet this requirement. On the market available crack‐bridging coating systems with a general technical approval are not usefull on concrete surfaces with high water contents (water saturation values of 90 %) as they may occur in floor slabs of watertight concrete constructions. Experiences with practical damage cases show, that with approved SPS 11‐systems osmotic induced bubbles may occur preferably on backside saturated floor slabs of watertight concrete constructions. In consequence the physical stresses of a coating (osmotic processes, capillarity reactions, hydraulic pressures as well as gas pressures) will be quantitatively estimated and compared with the capability of market systems. Alternative coating systems are presented and practical recommendations in order to avoid damages are given.     

Übergreifungsstöße von Betonstahl in selbstverdichtendem Beton

Load Carrying Capacity of Lap Splices in Self Consolidating Concrete This paper presents the results of experimental investigations on the load carrying capacity of lap splices under compression and tensile forces in self consolidating concrete (SCC). The test program consisted of four full scale beam tests and three column tests. It was concentrated on two common types of SCC, a powdertype concrete with limestone powder and a combination‐type concrete with fly ash. Depending on the specific lap length l_s/d_s the transmission mechanisms as well as the distribution of the bond‐, steel‐ and concrete stresses within the joint area were examined. The research project was sponsored by the German Association of Structural Concrete (DAfStb – V429).     

Zemente mit mehreren Hauptbestandteilen im Betonbau

Cements with Several Main Constituents in Concrete Construction – Sustainable Solutions for Building with Concrete In view of the reduction of climate‐related CO₂ emissions in the cement industry the manufacture of cements with several main constituents is of particular significance. One reason is the production process, which is more energy‐efficient and more ecological compared to “traditional” CEM I‐cements (Portland cements). But also the durability and performance in their use in concrete constructions are reasons why Portland‐composite cements (CEM II) and blastfurnace cements (CEM III) have meanwhile reached a market share of about 65% in Germany. For a few years now, approximately only 30% Portland cements have been used throughout Europe – with a continuous downward trend. The application‐specific properties, the possible areas of use as well as the ecologic advantages of the cements with several main constituents used in Germany so far are described in the following and illustrated by two practical examples. An outlook into possible further developments is given by examples of the performance of new cements in concrete.     

Wasserundurchlässige Bauwerke aus Beton

Watertight Concrete. About Planning and Execution The use of watertight concrete is regulated by the DAfStb‐Guideline. In practice this means that concrete buildings have to be erected as watertight structures. This method avoids the high costs of a bituminous sealing. It requires a clear predefinition of the use of the rooms, in order to define — on the basis of load and exposure — the concrete grade, arrangement of reinforcement, joint finishing, progress of concrete placement and seasoning. A proper structure can only be achieved, if the individual steps of the „quality assurance chain”︁ are dealed with continuously. Drying of the concrete and vapour diffusion should be taken into account for the later use.     

Verhalten feuerverzinkter Bewehrungsstähle in alkalischem Beton unter Berücksichtigung des Alkali‐ und Chromatgehaltes der verwendeten Zemente. Zusammenfassung des bekannten Wissens

Behaviour of galvanized Reinforcement in Alkaline Concrete in View of the Alkali‐ and Chromate‐Content of the used Cements Summery of the existing Knowledge If galvanized steel components are in contact with the alkaline environment of fresh concrete temporary zinc corrosion and hydrogen evolution may occur. This appearance is strengthened if instead of chromate containing cements chromate reduced cements are used. The corrosion reaction increases if cement with a high alkalinity is applied. The bond behaviour is continuously not negative influenced after present knowledge by the hydrogen evolution. However negative alterations of the concrete surface structure may occur as a consequence of rising hydrogen in the fresh concrete. This problem can be decreased if cements with lower alkalinity are applied.     

Fugenausbildung und ‐abdichtung bei wasserundurchlässigen Bauwerken aus Beton: Neue Regelwerke setzen Maßstäbe

Joint Design and Joint Sealing in Waterproof Concrete Structures – New Regulations are setting New Sealing Standards In many cases joints in structures of waterproof concrete turn out to be a weak point. For this reason they demand the care and attention of the designer and the contractor. A professional application as well by the planner as by the contractor is a decisive precondition for an effective operation of the joint sealing. New regulations like DAfStb‐code: “Waterproof concrete structures" and the German standard DIN V 18197: “Sealing of joints in concrete with waterstops" give details how the sealing systems should be used and dimensioned correctly. This article goes into the details of the new regulations and the basic rules for sealing.     

Stahlbetonträger mit Öffnungen. Ein vereinfachtes Bemessungskonzept

Reinforced Concrete Beams With Openings – A Simplified Design Concept – A comprehensive design concept for reinforced concrete beams with large openings was presented in Beton‐ und Stahlbetonbau 97, booklet 3, 2002. In recent years six laboratory tests were carried out to verify the design concept. Additionally extensive Finite Element computations with physically nonlinear material models were conducted to analyse the structural behaviour of reinforced concrete beams with opening groups. In this paper a simplified design concept for reinforced concrete beams with large openings and opening groups is presented which is based on the results of the test series and the FE‐computations.     

Bemessung von Fundamentplatten aus Stahlfaserbeton gemäß ÖVBB Richtlinie Faserbeton und DBV Merkblatt Stahlfaserbeton

Static Analysis and Verification of Steel Fibre Reinforced Concrete Foundation Slabs according to the Austrian Guideline “Fibre reinforced concrete” and DBV (German Concrete Association) Recommendations “Steel fibre reinforced concrete” Steel fibre reinforced concrete is used for foundation slabs of housing structures since many years. The Austrian guideline [1] and the DBV recommendations [2] provide material properties and design values for calculation and verification of steel fibre reinforced concrete structural members. This paper provides a comparative study on foundation slabs taking both guidelines into account. A nonlinear finite element parameter study has been performed in order to verify a simplified static calculation and verification method. This calculation method is based on the yield line theory. This paper concludes with a sample calculation for steel fibre reinforced foundation slabs according to the Austrian and German design recommendations.     

Bemessungsvorschlag für die verstärkte Querbewehrung bei mehrgeschossigen Ortbetonstützen ohne Übergreifungsstoß der Längsbewehrung. “Stumpfstoß von Ortbetonstützen”

Design and Construction of Butt‐Jointed in‐situ Concrete Columns The load bearing capacity of butt‐jointed in‐situ concrete columns was investigated at the University of applied science Gießen‐Friedberg. Experiments were carried out in the laboratory on test specimens. Afterwards the experiments were modeled and calculated with a finite element method program and a theoretical study was worked out. With the results an engineering model was developed.     

Untersuchungen zum Einfluss der Berechnungsmethode auf die Größe von Zwangschnittgrößen in Stahlbeton‐Tragwerken

Es wird anhand eines Rechenbeispieles gezeigt, dass die Größe von Zwangbeanspruchungen in Stahlbeton‐ und Spannbetontragwerken wesentlich von der zur Schnittkraftermittlung gewählten Berechnungsmethode abhängig ist und dass in Sonderfällen – z. B. zur Tragfähigkeitsbeurteilung älterer Bauwerke – eine nichtlineare Berechnung zur realistischen Erfassung von Zwangbeanspruchungen sinnvoll sein kann. Investigations on the Influence of Calculation Methods on the Dimension of Constraint Stresses in Reinforced Concrete Structures A calculation example shows, that the dimension of constraint stresses in reinforced concrete structures depends siginificantly on the calculation method used for the evaluation of stress‐resultants. In particular cases – e.g. assessment of the load‐bearingcapacity of older buildings – a nonlinear calculation is reasonable to have a realistic assessment of the contraint stresses.     

Stahlbetonschalen ohne Schalung – ein neuer Weg im Schalenbau

Reinforced Concrete Shells without Formwork – a new Approach to the Construction of RC‐Shells Diversity of designs, slenderness and elegance are the qualities of RC‐shells that leave one amazed at the sight of such structures. New architectural schools are currently about to induce a renaissance in shell structures, at least for public prestigious buildings. The main obstacle, that inhibits a more widely acceptance of those aesthetically pleasing shell‐structures is their cost of construction. One of the biggest cost‐factors in case of geometrically more complex designs is the construction of the formwork. Yet the placement of reinforcement and concrete turns out often to be equally complicated and thus costly. A new shell construction method developed at the Vienna University of Technology relies on post‐tensioning a RC‐membrane into a spatially bent shell, thus cutting the cost of construction considerably.     

Querschnittsberechnung von Stahlbetonstäben – Stand der Forschung

Cross‐Sectional Analysis of Reinforced Concrete Beams – State of the Art Many common structures consist of one‐dimensional members. For such structures beam theory is applicable. Within beam theory, the material behaviour can be captured on cross‐sectional level. Regarding reinforced‐concrete structures, material nonlinearity has generally to be considered. The present article provides an overview of the state of the art in cross‐sectional analysis of one‐dimensional reinforced‐concrete elements. A crosssectional analysis describes the relationship between the internal forces and the generalized strains. There is a large number of different models, for which a classification is suggested here. Existing models can be classified into resultant models, truss models, uniaxial models, wall models, and finite element models. For each class, the characteristics are outlined and the most important models are presented.     

Zur Tragfähigkeit unbewehrter Betonwände

Load Bearing Capacity of Non‐Reinforced Concrete Walls The simplified approach for the design of compression members made of non‐reinforced concrete according to DIN 1045‐1 leads to large cross sections for slender walls with eccentric loading. Based on the principles of DIN 1045‐1 a design method is deduced in this article. The use of this method allows a simple, standardised and economic design of non‐reinforced compression members. A further increase in load bearing capacity can be achieved by taking into account the concrete tensile strength.     

Zur Ermittlung der Normalkraft‐Verlängerung und Moment‐Krümmung‐Beziehungen der Stahlbetonbauteile im Grenzzustand der Gebrauchstauglichkei

Die Nachweise zur Begrenzung der Verformungen von Stahlbetonbauteilen sind infolge der Verwendung von Baustoffen höherer Festigkeiten immer wichtiger geworden, oft sogar maßgebend. Eine Verdopplung der Betondruckfestigkeit eines normalen Betons ruft eine etwa 20%ige Erhöhung des E_c‐Moduls hervor aber keine des Betonstahls, da E_s konstant ist. Dies und die dementsprechend schlanker gewordenen Stahlbetonbauteile führen zu größeren Verformungen – Verlängerungen, Durchbiegungen und/oder Verdrehungen – die deren Verhalten beeinträchtigen können. Die für die Ermittlung der Verformungen benötigten “Normalkraft‐mittlere Dehnungslinien”, bzw. “Moment‐mittlere Krümmungslinien” werden erläutert. About the Calculation of Displacements of Reinforced Concrete Members in the Serviceability Limit State The verification of reinforced concrete elements for the purpose of limiting deformations has become increasingly important, often even decisive, as a result of the use of higher strength materials. A doubling of the compressive strength of a normal concrete causes an increase of about 20% in the E_c‐module, and none of reinforcing steel, because E_s is constant. This and, accordingly, the slender reinforced concrete elements lead to larger deformations – elongations, deflections and/or rotations – which may affect their behaviour. The determination of “axial tensile force – mean strain diagrams”, respectively “bending moment – mean curvature diagrams”, needed for the calculation of the displacements, is explained.     

Beton erhöhter Brandbeständigkeit mit Polypropylenfasern: Nachweise im Frisch‐ und Festbeton

Increased Heat‐Resistant Concrete with Polypropylene Fibres: Testing Methods in set and unset Concrete The consequences of fires in tunnels in Austria and other countries resulted in seeking for more information on the effects of fires in tunnels on the concrete structure. The findings from different research programs led to a new guideline of the Austrian Society for Concrete, and Construction Technology (ÖVBB). By adding polypropylene fibres a spalling of concrete of the inner lining can be avoided successfully in tunnels even under the extreme condition of fires. An equal distribution of fibres in the concrete is essential for their effectiveness. To verify the distribution of fibres during construction, testing methods which are explained in the article at hand were developed. In addition, the conclusions derived from the practical use at a construction site are shown.